The present invention relates to a coupling and to a method for connecting an element such as a pipe to a coupling.
Many designs of couplings are known which seek to achieve a reliable sealed connection between the coupling and an element such as a pipe inserted into the coupling. Many known couplings rely upon mechanical compression of for example a deformable metal ring between a coupling socket and the outer surface of the pipe. Other couplings are known in which pipe to coupling seals are achieved using thermosetting intermediate components. The present invention is concerned with couplings which rely upon mechanical deformation of coupling components.
Mechanical couplings are used in circumstances in which it is often difficult to rely upon those responsible for assembling the couplings to carry out all the necessary procedures in a systematic manner. For example, where pipes to be interconnected are relatively easily deformable, for example HDPE pipes as widely used in the water and gas industries, it is necessary to push an insert into the end of a pipe to which a coupling is to be connected so as to prevent the pipe being excessively deformed radially inwards when the coupling is assembled, and with many couplings it is also necessary to position further components around the pipe which are not visible in the final assembly. External inspection of an assembled coupling does not enable the inspector to check that the insert and any other components have been properly positioned. It is also difficult to ensure that the pipe end inserted into a coupling is not contaminated with dirt to an extent which compromises coupling integrity. This is a real problem in circumstances in which mechanical couplings are used that rely upon only a limited axial interengagement between the external surface of the pipe and a radially compressed coupling element it is also not possible by visual inspection to check that sufficient force has been applied to coupling components to achieve a reliable interconnection. For example couplings which rely upon the application of a predetermined force by a crimping tool or relative rotation of a coupling body and a threaded compression element may appear on visual inspection to have been correctly assembled even if the required force has not been applied by the assembler.
A further problem with certain known couplings is that complex and cumbersome tools such as hydraulic presses are required for coupling assembly. This is particularly the case with large diameter couplings. Such tools cannot be readily used on-site, e.g. in trenches excavated to give access to buried pipes.
It is an object of the present invention to provide a coupling which enables the problems outlined above to be obviated or mitigated.
According to the present invention, there is provided a coupling comprising a tubular inner member defining a socket for receiving an element to which the coupling is to be connected, an outer member which extends around and defines an annular chamber with the inner tubular member, and an inlet communicating with the chamber to enable pressurisation of the chamber by introducing fluid to the chamber through the inlet, the inner member being radially compressible by pressurisation of the chamber to grip an element within the socket.
The invention also provides a method for connecting an element to a coupling comprising a radially compressible tubular member defining a socket into which the element is inserted, wherein a sealed chamber is defined around the tubular member, and pressurised fluid is introduced into the chamber, the pressure of the introduced fluid being sufficient to deform the tubular member radially inwards to grip the element.
With the coupling and method in accordance with the invention, the coupling is designed so that the user knows that providing sufficient pressure has been delivered to the coupling, the tubular inner member within the coupling socket will have been deformed to a sufficient extent to ensure a reliable connection. If the coupling is used with a readily deformable element such as an HDPE pipe, and no insert has been positioned within the pipe, the pipe will collapse under a relatively low applied pressure in a readily apparent manner. No other components can be accidentally omitted. Thus incorrect coupling assembly can be readily detected. Pressure can be applied up to a predetermined limit at which it is known from the design of the coupling that appropriate tube deformation has occurred. Alternatively, pressure can be applied until fluid leaks from a seal of the chamber, in which case seal failure can be taken as confirmation that the required pressure has been applied. For example a burst disc may be provided that will rupture when a predetermined pressure limit has been reached. The predetermined pressure limit may be for example 3000 psi (211 kg cmxe2x88x922). The pressurised fluid may be such that it sets inside the annular chamber so as to maintain support for the tubular inner member after the applied pressure is released The pressurised fluid may be delivered by a simple fluid pumping system.
Although the coupling has particular utility in connecting tubular pipes together, it could be used to make a connection to any element which could be inserted into the socket and which is dimensioned such that it is gripped after compression of the inner member.
Two seals may be located between the inner and outer members at positions spaced apart along the length of the inner tubular member and on opposite sides of the inlet, the seals closing ends of the annular chamber. The seals may comprise for example O-rings located between the inner and outer members, explosively welded joints, soldered joints, or brazed joints. Two pairs of seals may be provided, the seals of each pair defining a respective chamber communicating with a respective pressurised fluid inlet.
If means are provided for releasing pressurised fluid from the chamber if pressure within the chamber exceeds a predetermined limit, the pressurized fluid release means may comprise a burst disc incorporated in the outer member, or a seal between the inner and outer members which fail after a predetermined radial compression of the inner member.
The tubular inner member may define a radially inwards extending member to limit the depth of insertion of an element into the socket.
The outer member may be a tube of sufficient strength to resist expansion as a result of pressurisation of the chamber. Alternatively, the outer member is deformable and the inlet comprises means for engaging an opening in a support clamp within which the coupling may be received, the support clamp resisting radially outwards expansion of the outer member resulting from pressurisation of the chamber which communicates with the inlet. The inlet may comprise a tube extending through and radially outwards from the deformable outer member, the tube being adapted to be inserted into the clamp opening. The clamp opening may support a seal with which the inlet tube engages to prevent pressurisation fluid penetrating between the clamp and the deformable outer member.
Means may be provided for preventing loss of pressurisation fluid from the chamber. Such an arrangement is particularly suitable when the chamber is filled with a fluid which hardens after pressurisation of the chamber. The pressurisation loss preventing means may comprise a non-return valve in the inlet.
The tubular inner member may be a copper tube.
When the coupling is used with a deformable element such as a HDPE pipe, a tubular insert may be inserted into the end of the pipe, the insert being arranged to limit the radially inwards deformation of the pipe. The insert is preferably provided with surface formations to grip the pipe after radially inward deformation thereof, for example, circumferentially extending teeth, or circumferentially extending rectangular grooves, or openings extending radially through the insert. The insert may be attached to a flange. The end of the insert which is introduced first into the pipe may be outwardly flared, the length of the insert being less than the length of the socket, such that the portion of the pipe which is deformed radially inwards extends axially on both sides of the flared end of the insert.
The insert may have one end which in use is inserted inside the end of one of two pipes to be interconnected by the coupling and the other end of which in use is inserted inside the end of the other of the two pipes. The tubular insert may be ribbed to define an expansion joint to enable axial expansion and contraction of the tubular inset he tubular insert may be ribbed to limit the depth of insertion of the insert into the pipes.
A reinforcing member may be positioned inside the inner tubular member such that the reinforcing member is pressed radially against the element by pressurisation of the chamber. The reinforcing element may be a metal coil.
A reinforcing member may be positioned within the element during pressurisation of the chamber to prevent collapse of the element. The reinforcing member may comprise an insert which will be retained within the coupling and a removable body which is removed after pressurisation of the coupling. The removable body may comprise two interengageable wedge-shaped elements.